The present invention relates to transportation drums and more particularly to a novel drum for transportation of a long and continuous length of a flexible electric power cable.
Flexible cables capable of carrying voltages in excess of 230 KV. are gaining increased industrial acceptance, particularly for underground installation. The extremely high voltage (EHV) cables have relatively large diameters due to the increased thickness of the insulation required. Cables of the gas-insulated type, especially, may eventually be produced with outer diameters as large as 18 inches. The largest diameter flexible cable presently available, and which is capable of being wound upon a drum has an outer diameter of about 6 inches and is used for radio frequency power transmission purposes. A useful continuous length of this relatively "small" cable can be wound on a correspondingly "small" drum and easily shipped. As the outer diameter of the cable increases, the continuous length of cable which can be wound upon a drum for transportation from the plant of the cable manufacturer to the installation location decreases. Due to road and rail clearance limitations, the cable drums can have a maximum diameter of the order of 12-15 feet, to allow passage beneath overpasses and tunnels, and a maximum width of 8 feet, to prevent drum overhang into an adjacent track or traffic lane. The dimension restrictions on the cable drum so severely limit the practical continuous winding length of cable which can be wound upon a single drum for shipment that cables with an outer diameter greater than 9 inches cannot be drum wound and must instead be shipped in straight lengths. Thus, several relatively short continuous cable lengths, each of the order of 40 feet long, must be spliced on-site to provide a desired length of EHV cable for installation. Such on-site splicing is expensive and time consuming since contaminating matter which may eventually cause electrically weak points to develop along the length of the cable must be excluded during splicing.
It is desirable to provide a drum on which a relatively large diameter flexible electrical power cable can be wound and to enable transportation of as long a continuous length of this previously non-drum-transportable corrugated cable as possible, without exceeding the maximum height and width dimensions imposed by transportation requirements.